Kconfig: Move CONFIG_DESIGNWARE_ETH to Kconfig

Move this to Kconfig and clean up board config files that use it. Also
rename it to CONFIG_ETH_DESIGNWARE to fit with the naming that exists
in drivers/net/Kconfig.

Signed-off-by: Simon Glass <sjg@chromium.org>
Version 1:
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/board/spear/spear310/spear310.c b/board/spear/spear310/spear310.c
index a4c6a8e..6f39ef1 100644
--- a/board/spear/spear310/spear310.c
+++ b/board/spear/spear310/spear310.c
@@ -52,7 +52,7 @@
 {
 	int ret = 0;
 
-#if defined(CONFIG_DESIGNWARE_ETH)
+#if defined(CONFIG_ETH_DESIGNWARE)
 	u32 interface = PHY_INTERFACE_MODE_MII;
 	if (designware_initialize(CONFIG_SPEAR_ETHBASE, interface) >= 0)
 		ret++;